1. Field of the Invention
The present invention relates to a connection structure of connecting an electric wire and a terminal by applying an ultrasonic vibration to the electric wire and the terminal.
2. Description of the Related Arts
Japanese Patent Application Laid-Open No. 7-70345 discloses a structure in which a covering portion of a covered electric wire is molten and removed by applying an ultrasonic vibration to these electric wire and terminal so as to conductively contact with a core wire of the covered electric wire and a terminal.
FIG. 1A and FIG. 1B each show a connector having a conventional structure in which a first member 1 and a second member 2 made of a resin face each other.
An upper surface of the first member 1 is formed with a groove portion 3 along a longitudinal direction thereof, and a small concave portion 4 is formed along a longitudinal direction of the groove portion 3 with a given interval. A terminal 5 is inserted into the groove portion 3 of the first member 1 along a longitudinal direction of the groove, and then, a covered electric wire 6 is placed on the terminal 5. The covered electric wire 6 is placed on the terminal 5 in a state that many core wires thereof are covered with a covering portion made of resin.
A lower surface of the second member 2 is formed with a protrusion 7 which is fitted into the groove portion 3 of the first member 1 and a small convex portion 8 which is fitted into the concave portion 4 of the groove 3, along the longitudinal direction thereof.
These members having the aforesaid structure is assembled in the following manner. More specifically, the terminal 5 and the covered electric wire 6 are inserted into the groove portion 3 of the first member 1, and then, in this state, the protrusion 7 of the second member 2 is fitted into the groove portion 3 of the first member 1 so that the terminal 5 and the covered electric wire 6 are pressed down by means of the second member 2 and the first member 1. At this time, the terminal 5 and the covered electric wire 6 are partially bent at a place where the concave portion 4 and the convex portion 8 are mutually fitted, so that these terminal and covered electric wire can be prevented from coming off.
And then, in a state that these terminal 5 and covered electric wire 6 are held between the first member 1 and the second member 2, ultrasonic vibration is applied to these members from an ultrasonic horn (not shown) while pressurizing them. A covering portion of the covered electric wire 6 is melted and removed by a heat generated by the ultrasonic vibration, and therefore, an internal core wire is exposed, and thus, the exposed core wire and the terminal 5 conductively contact with each other. With this conductive contact, the first member 1 and the second member 2 are integrally connected, so that a connector housing the terminal 5 and the electric wire can be provided.
FIG. 2 shows an example converse to FIG. 1A and FIG. 1B. More specifically, a small convex portion 8 is formed in the groove portion 3 of the first member 1, and a small concave portion 4 fitted into the convex portion 8 is formed in the second member 2. Likewise, in this case, in the state that the terminal 5 and the covered electric wire 6 are held between the first member 1 and the second member 2, by applying the ultrasonic vibration thereto, it is possible to conductively contact the core wire with the terminal 5.
FIG. 3 shows a structure for preparing a multi-polar connector, and the first member 1 is formed with a plurality of groove portions 3; on the other hand, the second member 2 is formed with a plurality of protrusions 7 which face the groove portions 3. After the terminal is housed in the respective groove portions, the covered electric wire is placed on the terminal, and thereafter, in a state that these terminal and electric wire are held between the first member 1 and the second member 2, the ultrasonic vibration is applied to them while pressurizing the same to thereby prepare a connector.
FIG. 4 shows a state that the terminal and the covered electric wire 6 are held between the first member 1 and the second member 2 having the structure as described above. And then, these terminal 5 and the covered electric wire 6 are pressed down by the protrusion of the second member 2 so as to be overlapped each other, and thus, bent portions 5a and 6a corresponding to the convex portion 8 and the concave portion 4 are formed to prevent these terminal and covered electric wire from coming off.
However, according to the conventional structure, the core wire of the covered electric wire does not sufficiently contacts with the terminal; for this reason, the conventional structure has a problem that a contact resistance becomes large. FIG. 5 shows an ideal state that a core wire 9 of the covered electric wire and the terminal 5 contact with each other by ultrasonic vibration. More specifically, the covering portion of the covered electric wire is melted and removed, and then, the core wires 9 are exposed and contacts with the terminal 5 in a state of coming into line. Further, the exposed core wires 9 are held down by means of the protrusion 7 of the second member 2 so as to keep this contact state. At this time, the groove portion 3 is filled with the melted and removed covering portion, as shown by a reference numeral 10, and this serves to couple the first member 1 with the second member 2.
In actual fact, the protrusion 7 is softened by a heat generated when the covering portion of the covered electric wire is melted; as a result, as shown in FIG. 6, a distal end portion 7a of the protrusion 7 is formed. By the deformation of the protrusion 7, it is impossible to hold down the core wires 9, nd the core wires 9 come loose in a row; for this reason, these ore wires 9 can not sufficiently contact with the terminal 5. As a result, a contact area is reduced, and a contact resistance becomes large.
In such a case, there is made a proposal of forming the second member 2 including the protrusion 7 of a resin having high heat-resistance. However, the high heat-resistant resin is expensive, and it is difficult to mold the resin; for this reason, precision is lowered. Further, the melted covering portion of the covered electric wire and the second member 2 are not effectively joined together; for this reason, there is a problem that these members are firmly assembled.